1.Field of the Invention
The invention relates generally to an apparatus that facilitates vascular access for patients. In particular, the invention relates to an extended use tubing apparatus that is inserted into a patient to facilitate vascular access for chronic hemodialysis treatment. The tubing provides an arteriovenous fistula that resists occlusion and/or clogging.
2. Known Art
Over 130,000 patients undergo chronic hemodialysis in the United States each year as treatment for renal failure. Conventional hemodialysis treatment requires extensive and often extended, long-term vascular access. Access to the blood supply is generally sought through the vasculature, which is usually accomplished by establishing a native artery to vein arteriovenous fistula or by placement of a prosthetic graft fistula.
The Brescia-Cimino direct radio-cephalic fistula is a preferred form of permanent access to the vasculature. In this surgery, and in other native arteriovenous fistulas a communication is established between an artery traversing a limb (i.e. the arm or leg) and a corresponding vein in the same limb. If acceptable vasculature is not available then a prosthetic graft is employed to create a fistula for vascular access. Unfortunately, all types of vascular access are known to have a high failure rates and associated high costs of treatment. Vascular access often eventually fail due to the formation of scar tissue inside the vessel or due to vessel occlusion. Other common causes of graft failure are technique errors, infection, and neointimal hyperplasia at the distal anastomosis (venous) and within polytetraflouroethylene (PTFE) graft segments. Hyperplasia or buildup of fibrin at the venous anastomosis is probably the leading threat to most A-V fistulas. Arterial occlusive problems are less commonly the primary cause of fistula failure. As will be readily appreciated by those skilled in the art, failure of hemodialysis access contributes to morbidity, hospitalization time, and the cost of treatment.
While percutaneous interventional techniques (such as angoiplasty, atherectomy, and stent placement) are becoming increasingly popular in the management of hemodialysis access graft complications, these techniques are also generally prone to failure for the same reasons as the original fistula, necessitating further surgical revision. Such revision usually consists of the implanting of a PTFE interposition graft, and offer 30-day patencies of about 44-65%.
PTFE interposition grafts are also often placed in patients who have failed native fistula. Usually, these fistulae retain a small segment of patent vein beyond the anastomosis, and have reconstitution of veins further up the arm via collaterals. An interposition prosthetic graft is used to bridge the artery and vein.
Various types of highly flexible, non-porous tubings have been previously proposed for various medical applications. These applications typically involve the insertion of the tubing into a living body, either temporarily or as a permanent implant. Temporary applications include the use of the tubing as a catheter tubing to convey fluids into or out of a body, or alternatively as the tubing portion of a medical device such as an endoscope. For example, present endoscope channel tubes are made of porous expanded PTFE having a microstructure of nodes interconnected by fibrils, made as taught by U.S. Pat. Nos. 4,187,390 and 3,953,566.
These tubes typically have a very small pore size with a fibril length of less than five microns. They are quite flexible, inert, biocompatible and lubricious. However, due to the porosity of the tubing, during use various contaminants such as proteins and calcium tend to penetrate the void spaces present on the inner surface of the tube and to adhere to the inner surface. The adhesion of contaminants to the inner surface of the tube result in a decline in the slip properties of the inner surface, and also impaired other tube functions such as its flexing properties. Moreover, washing and sterilization were necessary in order to remove the contaminants so that the tube could be reused and such washing and sterilization were time consuming, and represented a burdensome operation.
Thus, there exists a need in the art for an improved apparatus for establishing reliable, long-term access to a patient's vasculature for chronic hemodialysis treatment. In particular, there exists a need for a fistula that facilitates subsequent remedial revisions including the removal and/or replacement of portions of the tubing. An ideal tubing should promote uninhibited blood flow through the tubing while resisting clogging or other occlusions.